A light traffic load in the en route sector influenced the controller to concentrate his visual scan on the one aircraft being controlled. This concentration on one area of the radar display reduced the controller's ability to maintain full situational awareness as to the position of this flight in relation to the various lines depicting different MVA boundaries. As ABL814 approached the 14 000-foot MVA line on the controller's radar display, the aircraft was well below the usual 16 000- to 17 000-foot altitude associated with that line and was levelling at an altitude that is normally associated with an aircraft approaching the 11 000-foot MVA line. At the time he made the error, the controller was focussed on the aircraft target. He saw that the aircraft was approaching an MVA line, he knew that he had already given a descent clearance to 14 000 feet asl, and he recognized from the altitude display that the aircraft was levelling at that altitude. When the aircraft crossed the MVA line, the controller gave the next step-down clearance to an altitude of 11 000 feet asl; this was done out of habit and without realizing that the aircraft was actually further north than normal and entering the 14 000-foot MVA area. After clearing the aircraft to 11 000 feet asl, the controller increased his range of visual scan in preparation for handing off the aircraft to the arrival controller. It was at that point that he realized the aircraft's position was much further north than expected. The crew of ABL814 was unaware of the controller's error and accepted the clearance and descended to the altitude issued by the controller, which was below the MVA for the area in which the aircraft was flying. This action was not in accordance with the CAR, but was consistent with a control procedure that was being used routinely by the Vancouver ACC, and that had been approved for use by Transport Canada. When operating below published minimum altitudes, there is no independent means for aircrew to easily cross-check MVA boundaries with published information available in the cockpit; therefore, the crew's ability to recognize or compensate for the controller's error was greatly reduced. The crew's response to the loss of direct controller-pilot communication, after levelling at 11 000 feet asl, was influenced by the fact they were operating in VMC. Based on the pilot's knowledge of the area north of Vancouver, he had come to expect sporadic radio coverage in the high terrain and, because these communication difficulties were normally encountered and therefore anticipated, he did not consider them to be valid communication failures. As a result, his motivation to initiate the loss of communication procedures published in the CFS was reduced. The arrival controller was not informed of the communication problem being attended to in the en route sector. Had the en route controller anticipated that the aircrew would try to contact the next sector on its route of flight and had the arrival controller known about the problem, the arrival controller could have directed the aircraft to climb immediately on initial contact. MVAs are non-published minimum IFR altitudes to which a pilot cannot make reference in the cockpit. Accepting an MVA when that aircraft is not being radar vectored can lead to confusion about whether the pilot or the controller has responsibility for obstacle and terrain clearance. Additionally, an error by the controller in assigning an incorrect altitude cannot be cross-checked by the pilot, and could result in an aircraft descending below a minimum IFR altitude. Local interpretation of existing rules and procedures can lead to an erosion of the defences designed to provide minimum acceptable obstacle and terrain clearance for aircraft in flight. Another defence, which would have alerted the controller much sooner to the descent by ABL814 below the minimum IFR altitude, would have been MSAW. This system, already available in other ATC systems worldwide, and slated to be installed as part of the RAMP radar as early as 1990, is still not available to aircraft flying in civil controlled airspace in Canada. NAV CANADA has not been able to deploy this capability to date.Analysis A light traffic load in the en route sector influenced the controller to concentrate his visual scan on the one aircraft being controlled. This concentration on one area of the radar display reduced the controller's ability to maintain full situational awareness as to the position of this flight in relation to the various lines depicting different MVA boundaries. As ABL814 approached the 14 000-foot MVA line on the controller's radar display, the aircraft was well below the usual 16 000- to 17 000-foot altitude associated with that line and was levelling at an altitude that is normally associated with an aircraft approaching the 11 000-foot MVA line. At the time he made the error, the controller was focussed on the aircraft target. He saw that the aircraft was approaching an MVA line, he knew that he had already given a descent clearance to 14 000 feet asl, and he recognized from the altitude display that the aircraft was levelling at that altitude. When the aircraft crossed the MVA line, the controller gave the next step-down clearance to an altitude of 11 000 feet asl; this was done out of habit and without realizing that the aircraft was actually further north than normal and entering the 14 000-foot MVA area. After clearing the aircraft to 11 000 feet asl, the controller increased his range of visual scan in preparation for handing off the aircraft to the arrival controller. It was at that point that he realized the aircraft's position was much further north than expected. The crew of ABL814 was unaware of the controller's error and accepted the clearance and descended to the altitude issued by the controller, which was below the MVA for the area in which the aircraft was flying. This action was not in accordance with the CAR, but was consistent with a control procedure that was being used routinely by the Vancouver ACC, and that had been approved for use by Transport Canada. When operating below published minimum altitudes, there is no independent means for aircrew to easily cross-check MVA boundaries with published information available in the cockpit; therefore, the crew's ability to recognize or compensate for the controller's error was greatly reduced. The crew's response to the loss of direct controller-pilot communication, after levelling at 11 000 feet asl, was influenced by the fact they were operating in VMC. Based on the pilot's knowledge of the area north of Vancouver, he had come to expect sporadic radio coverage in the high terrain and, because these communication difficulties were normally encountered and therefore anticipated, he did not consider them to be valid communication failures. As a result, his motivation to initiate the loss of communication procedures published in the CFS was reduced. The arrival controller was not informed of the communication problem being attended to in the en route sector. Had the en route controller anticipated that the aircrew would try to contact the next sector on its route of flight and had the arrival controller known about the problem, the arrival controller could have directed the aircraft to climb immediately on initial contact. MVAs are non-published minimum IFR altitudes to which a pilot cannot make reference in the cockpit. Accepting an MVA when that aircraft is not being radar vectored can lead to confusion about whether the pilot or the controller has responsibility for obstacle and terrain clearance. Additionally, an error by the controller in assigning an incorrect altitude cannot be cross-checked by the pilot, and could result in an aircraft descending below a minimum IFR altitude. Local interpretation of existing rules and procedures can lead to an erosion of the defences designed to provide minimum acceptable obstacle and terrain clearance for aircraft in flight. Another defence, which would have alerted the controller much sooner to the descent by ABL814 below the minimum IFR altitude, would have been MSAW. This system, already available in other ATC systems worldwide, and slated to be installed as part of the RAMP radar as early as 1990, is still not available to aircraft flying in civil controlled airspace in Canada. NAV CANADA has not been able to deploy this capability to date. The en route controller accepted an early radar handoff on ABL814 when the aircraft was about 20 nautical miles north of his sector; this increased the time the aircraft was under his control. The en route controller descended the aircraft early to facilitate a four-minute flow delay required by the terminal specialty; this early descent modified the aircraft's approach profile and lowered its crossing altitudes over two MVA lines. When ABL814 crossed the en route sector's 14 000-foot MVA line, the en route air traffic controller inadvertently cleared the pilot to descend to 11 000 feet asl, an altitude that was appropriate for the southern MVA line. There is no clear definition in applicable publications for the term communication failure. The Vancouver ACC was using an altitude assignment procedure which allowed controllers to assign altitudes that were below the minimum published IFR altitudes; Transport Canada had approved the use of this procedure. The controller assigned an inappropriate MVA to an aircraft that was not being radar vectored. The crew of ABL814 descended below the MVA as directed; there is no way for the aircrew to cross-check the MVA boundaries. An MSAW system is designed to alert the controller of an error; NAV CANADA has not yet implemented this type of independent warning into its control system. The controller's attempts to recover from the error were impeded by a lack of direct controller-pilot communications capability because of the aircraft's low altitude; specifically, ABL814 could not be contacted directly using NAV CANADA's ground-based communications network. The crew of ABL814 routinely lost radio coverage when approaching Vancouver and, therefore, were not predisposed to implement the lost communication procedures as prescribed in the Canadian Aviation Regulations (CAR). The Vancouver arrival controller, who handles the adjacent airspace, is physically separated from the en route controller's workstation, and he had not been informed of the communications problem being addressed in the en route sector. The arrival controller received a transmission from ABL814 but, because he was unaware of the communication problem, directed the crew to return to their previously assigned en route frequency. MVA charts do not require flight inspection certification and TP 308 makes no direct mention of a requirement for direct pilot-to-controller communication capabilities either at or below the MVA. Weather at the time was VMC. There was no risk of collision with terrain because the crew could see the mountains.Findings The en route controller accepted an early radar handoff on ABL814 when the aircraft was about 20 nautical miles north of his sector; this increased the time the aircraft was under his control. The en route controller descended the aircraft early to facilitate a four-minute flow delay required by the terminal specialty; this early descent modified the aircraft's approach profile and lowered its crossing altitudes over two MVA lines. When ABL814 crossed the en route sector's 14 000-foot MVA line, the en route air traffic controller inadvertently cleared the pilot to descend to 11 000 feet asl, an altitude that was appropriate for the southern MVA line. There is no clear definition in applicable publications for the term communication failure. The Vancouver ACC was using an altitude assignment procedure which allowed controllers to assign altitudes that were below the minimum published IFR altitudes; Transport Canada had approved the use of this procedure. The controller assigned an inappropriate MVA to an aircraft that was not being radar vectored. The crew of ABL814 descended below the MVA as directed; there is no way for the aircrew to cross-check the MVA boundaries. An MSAW system is designed to alert the controller of an error; NAV CANADA has not yet implemented this type of independent warning into its control system. The controller's attempts to recover from the error were impeded by a lack of direct controller-pilot communications capability because of the aircraft's low altitude; specifically, ABL814 could not be contacted directly using NAV CANADA's ground-based communications network. The crew of ABL814 routinely lost radio coverage when approaching Vancouver and, therefore, were not predisposed to implement the lost communication procedures as prescribed in the Canadian Aviation Regulations (CAR). The Vancouver arrival controller, who handles the adjacent airspace, is physically separated from the en route controller's workstation, and he had not been informed of the communications problem being addressed in the en route sector. The arrival controller received a transmission from ABL814 but, because he was unaware of the communication problem, directed the crew to return to their previously assigned en route frequency. MVA charts do not require flight inspection certification and TP 308 makes no direct mention of a requirement for direct pilot-to-controller communication capabilities either at or below the MVA. Weather at the time was VMC. There was no risk of collision with terrain because the crew could see the mountains. The controller inadvertently cleared ABL814 below the MVA, and the crew accepted the clearance. Contributing to this occurrence were the lack of direct controller-pilot communication capability because of the aircraft's low altitude, and a reduced motivation by the flight crew to respond to the loss of communication because of the routine nature of this event.Causes and Contributing Factors The controller inadvertently cleared ABL814 below the MVA, and the crew accepted the clearance. Contributing to this occurrence were the lack of direct controller-pilot communication capability because of the aircraft's low altitude, and a reduced motivation by the flight crew to respond to the loss of communication because of the routine nature of this event. NAV CANADA is aware of the communication problems north of Vancouver and is installing a new transmitter on Saltspring Island to increase the communication coverage in that area. Air BC requested a copy of the MVA charts for Vancouver and has made this information available to its flight crews to increase their general knowledge. TP 308 is currently under revision; the new edition will specify that MVAs must include sufficient communications coverage to permit direct controller-pilot communication (DCPC) at all times. Transport Canada notes that increasing emphasis is being placed on allowing aircraft to self-navigate along published routes, especially in terminal areas. Because of these evolutions in operational procedures, Transport Canada has indicated that a literal application of CAR 602.124 in its current form would place severe operational restrictions on both air traffic controllers and pilots. Transport Canada intends to submit a Notice of Proposed Amendment (NPA) on CAR 602.124 to include the notion of MVA application as it is currently being practised. The Board is concerned that NAV CANADA has no MSAW/CA installation dates assigned to its Corporate Safety Plan 1998/1999, notwithstanding NAV CANADA's ongoing commitment to the program.Safety Action NAV CANADA is aware of the communication problems north of Vancouver and is installing a new transmitter on Saltspring Island to increase the communication coverage in that area. Air BC requested a copy of the MVA charts for Vancouver and has made this information available to its flight crews to increase their general knowledge. TP 308 is currently under revision; the new edition will specify that MVAs must include sufficient communications coverage to permit direct controller-pilot communication (DCPC) at all times. Transport Canada notes that increasing emphasis is being placed on allowing aircraft to self-navigate along published routes, especially in terminal areas. Because of these evolutions in operational procedures, Transport Canada has indicated that a literal application of CAR 602.124 in its current form would place severe operational restrictions on both air traffic controllers and pilots. Transport Canada intends to submit a Notice of Proposed Amendment (NPA) on CAR 602.124 to include the notion of MVA application as it is currently being practised. The Board is concerned that NAV CANADA has no MSAW/CA installation dates assigned to its Corporate Safety Plan 1998/1999, notwithstanding NAV CANADA's ongoing commitment to the program.